1. Field of the Invention
The present invention relates to a small electronic device such as a personal computer or a word processor, and more particularly to a small electronic device which has a plurality of removable batteries.
2. Description of the Related Art
Recent years have seen the development of a variety of so-called lap top computers, which are basically portable personal computers.
Some typical models of lap top personal computers are provided with a foldable flat type display, such as a plasma display, which is freely rotatable between a closed position and an open position with respect to the main body of the computer. The plasma display can be folded down onto the main body to a closed position, such that it covers the keyboard which is integral with the main body of the computer. This feature, together with its relatively light weight and compact dimensions, makes the device easy to carry around from place to place.
To further improve their portability, some recently-developed lap top computers employ a battery such that they can be used even if the commercial power source is not available. In a case where the capacity of the battery is low, the operator is required to remove the battery from the main body of the computer and to charge or replace it. Because the lap top personal computer cannot be operated unless a commercial power source is used while the battery is being charged or replaced, places where the lap top computer can be used will be limited to places where commercial power can be made available.
With this in mind, lap top personal computers equipped with two batteries have been developed to improve the portability thereof. In a lap top computer of this type, it is possible to operate the lap top computer by using one of the two batteries as its power source even if the capacity of the other battery is low and that battery is removed from the computer for charging or replacement. The switching from one battery to the other battery to be used as a power source for the computer, that is, the switching from the battery in use as a power source to the battery not in use, is carried out automatically when the battery being used is removed from the main body of the computer. That is to say, the lap top personal computer detects, by means such as a microswitch, that the battery being used as a power source has been removed from the main body of the computer and switches the battery to be used as a power source from the removed battery to the other battery.
However, in switching these batteries, if the timing to switch from one battery to the other should be delayed by even a fraction of a second when the battery in use is removed from the main body of the computer, malfunctions or erasure of various data of the lap top personal computer will result due to the power supply to the lap top personal computer being discontinued for a short time if the timing to switch to the other battery is delayed.
For this reason, in a lap top personal computer provided with two batteries, when the battery in use is to be removed from the main body of the computer for charging or replacement thereof, so as to prevent conditions such as the erased data from occurring even when the power supply is stopped, it is necessary for the operator to accomplish troublesome operations such as storing the necessary data in such means as a magnetic disc unit before he or she removes the battery from the computer.
On the other hand, in order to prevent the power supply to the lap top computer from being interrupted, a method has been designed in which a power source is always supplied to the computer not only from the battery being used as a power source but also from the battery which is not in use. With this method, it is possible to prevent conditions such as erased data, because the power supply to the computer is not interrupted even when replacing the battery. However, because wasteful electric power is always consumed from the battery not in use as a power source, the life of the battery which is not used as a power source is reduced.